Glass cutting using a direct-current torque motor

ABSTRACT

A cutter head in a glass-cutting machine is rigidly connected to a movable member within a constant-reluctance motor. Current is supplied to the motor to move the member and therefore actuate the cutter head. In a preferred embodiment, the constantreluctance motor is a direct-current torque motor and the movable member is its rotor. In this embodiment, the cutter is downstream of the location of the axis of the rotor as the cutter scores the glass. Score lines of predetermined depth are obtained, despite small variations in thickness of the glass, and without the use of a pneumatic system that is slow-acting and difficult to maintain. Pressure exerted by the cutter head responds rapidly to changes in the current supplied to the motor, making it possible to vary the depth of the score desired during the making of a pattern cut, which could not be done with pneumatic or springloaded means of the prior art.

United States Patent Bier GLASS CUTTING USING A DIRECT-CURRENT TORQUEMOTOR David A. Bier, MeadowlandsJPa.

PPG Industries, Inc., Pittsburgh, Pa.

Mar. 26, 1971 Inventor:

Assignee:

Filed:

Appl. No.:

References Cited UNITED STATES PATENTS Primary ExaminerFrank T. YostAttorney-Chisholm & Spencer [5 7] ABSTRACT A cutter head in aglass-cutting machine is rigidly connected to a movable member within aconstantreluctance motor. Current is supplied to the motor to move themember and therefore actuate the cutter head. In a preferred embodiment,the constantreluctance motor is a direct-current torque motor and themovable member is its rotor. In this embodiment, the cutter isdownstream of the location of the axis of the rotor as the cutter scoresthe glass. Score lines of predetermined depth are obtained, despitesmall variations in thickness of the glass, and without the use of apneumatic system that is slow-acting and difficult to maintain. Pressureexerted by the cutter head responds rapidly to changes in the currentsupplied to the motor, making it possible to vary the depth of the scoredesired during the making of a pattern cut, which could not be done withpneumatic or spring-loaded means of the prior art.

17 Claims, 6 Drawing Figures rlO PAIENUI'EDSEPZEW v snwaurz ATTORNEYSGLASS CUTTING USING A DIRECT-CURRENT TORQUE MOTOR BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to thecutting of glass.

2. Description of the Prior Art Various equipment is known for thecutting of glass, such as U. S. Pat. Nos. 3,107,834; 3,146,926;3,151,794; and 3,253,756. In none of the foregoing is there used theconcept of actuating a cutting head by means of a motor that exerts uponthe glass being cut a force that remains substantially constant or isvaried at will in a desired and predetermined manner because of the useof a constant-reluctance motor means. Instead, it has been usual in theart of cutting glass to urge the cutter head against the glass either byspring-loaded means or by means of a pneumatic cylinder. Bothspring-loaded means an pneumatic-cylinder means have substantialdrawbacks. Spring-loaded means are not capable of being adjusted rapidlywhile a cut is in progress, e.g., in the cutting of a shape such as awindshield blank, so as to exert greater or lesser pressure and generatea score of greater or lesser depth, respectively, in the vicinity of acorner. Pneumatic means have the drawback that they are costly toinstall and maintain and that they are relatively slow-acting so that itis not ordinarily possible with such pneumatic means to change, asdesired, the intended depth of the score.

The broad concept of electrically or electromagnetically moving a cutterhead that is used in the cutting of glass is not novel. In thisconnection, reference is made to U. S. Pat. No. 1,856,128 to J. L. Drakeand U. S. Pat. No. 3,276,302 to T. A. Insolio.

The Drake reference states, for example, the cutters 15 are adapted tobe controlled by means of electromagnets 35, a pair of these magnetsbeing preferably though not necessarily provided for each cutter andupon energization thereof, the corresponding cutter or cutters 15 areadapted to be rocked on shaft 14 whereby the cutting tool 29 will belowered into operative or cutting position. (Page 2, lines 45-53). Thereference further states, Encircling rods 38 and 39 and bearing againstarm 16 and nuts 40 are compression springs 41 which serve to yieldablymaintain the cutting tool in engagement with the glass sheet during thecutting thereof whereby to automatically compensate for any inequalitiesin the surface thereof and further to maintain a constant pressure uponthe glass to uniformly score the same. (Page 2, lines 65-73).

Insolio discloses, for example, a solenod is mounted on a frame and whenenergized extends a pillar post holder and the pillar post downwardly sothat the cutting wheel of the pillar post' engages and scores relativelymoving sheets .of glass." (Column 2, lines 67-71).

The problem, however, with prior devices that were employed to maintaincutting forces is that as the cutter encounters variations in glassthickness or undulations due to warping, the air gap in these prior-artdevices changes, resulting'in a very large change in the applied cuttingforce. It is by no means unusual for the thickness of the glass beingcut to vary a few thousandths of an inch, yet even such relatively smallvariations in the cutting of pieces of glass having a thickness betweenabout 0.08 and 0.50 inches (about 2 and 12 millimeters, respectively),is likely to lead to considerable variations in the depth of score.There has been, of course, the possibility of using in the vicinity ofthe cutting wheel a reference wheel that is intended to ride upon theupper surface of the glass being scored, but it has ordinarily beenimpossible to arrange for any variation in the spacing between suchreference wheel and the cutting wheel while the cut is in progress,since means sufficiently fast-acting to permit such adjustment to bemade in the depth of the score being produced has been unknown, prior tothe instant invention.

It may be considered that direct-current torque motors are, per se,already known. Such devices comprise a rotor of permanent-magnetmaterial of high permeability, suitably keyed to a shaft. In operativeassociation with the permanent-magnet rotor, there are provided aplurality of coils actuated by a variablemagnitude direct-currentsource, such that when currnt is fed to the coils, there is a tendencyfor the permanent-magnet rotor to assume a home position, and such thatwhenever the permanent-magnet rotor is away from said home position,there is exerted upon the shaft a torque proportional to the magnitudeof the direct-current potential provided to the .abovementioned coils.

SUMMARY OF THE INVENTION Cutter heads in a glass-cutting machine areattached to a shaft that is rigidly connected to a rotor of adirectcurrent torque motor having a constant reluctance. Score lines ofpredetermined depth are obtained, despite small variations in thethickness of the glass, and without use of a pneumatic system that isslow-acting and difficult to maintain. The pressure exerted by thecutter head responds rapidly to changes in directcurrent potentialsupplied to the torque motor, making it possible to vary the depth ofthe score as desired dur ing the making of a pattern cut, which couldnot be done with the pneumatic or spring-loaded means of the prior-artdevices. After the score line is applied to the glass, a bending momentis applied about the score line to sever a piece of glass. It will beapparent to one skilled in the art that there are numerous devicescommerically available to apply such a bending moment.

In some situations, such as where the cutter has a sharp cutting angleand is applied to the glass under relatively high pressure, the cuttercreates a fracture that extends to the bottom of the surface of theglass and a bending moment is not necessary to sever a piece of glass.

DESCRIPTION OF THE DRAWINGS A complete understanding of the inventionmay be obtained from the foregoing and following description thereof,taken in conjunction with the appended drawings, which are diagrammaticand not to scale, unless noted, and in which:

FIG. 1 is a diagram indicating a cutting apparatus according to thepresent invention scoring a sheet of glass;

FIG. 2 is a diagram illustrating a circuit used to supply current to themotor;

FIG. 3 is a side view of the cutter head assembly shown in FIG. 1 bothbefore and during the scoring operation;

FIG. 4 is a diagram of a cutter head assembly;

FIG. 5 is a diagram of a block used to mount the cutter head to theshaft of FIG. 3; and

FIG. 6 is a diagram illustrating a shaft used to mount the cutter headto the rotor of the motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT trated, this is merely anexample and the number of motors is determined by the torque required toprovide a suitable force to the glass, and the capacity of each motor.For example, if each torque motor supplies a torque of 100 inch-ouncesand the effective moment arm is 74 of an inch, a scoring force of about17 pounds is supplied to the cutter. This force can be varied byadjusting the current supplied to the motor or the size of the momentarm. Further, although a rotary-type torque motor has been illustrated,the invention should not be limited to such a motor. A linear-typetorque motor (where the movable member slides with respect to thestationary member) may also be used, with the cutter assemby attached tothe movable member. Here, however, there is a higher inertia requiredthan in the rotary-type torque motor. The rotary-type torque motor has atrailing-arm effect. In other words, the cutter is downstream of thelocation of the axis of the rotor as the cutter scores the glass. Anyvariation in the location of the glass surface will cause the cutter topivot about the axis, and this exhibits less inertia than is necessaryto move vertically a cutter attachedto a linear-type torque motor. Thisis because the moment of inertia of a mass against rotation is lowerthan its moment of inertia against translation.

Referring to FIG. 2, a direct-current torque motor, indicated generallyas 10, may be considered as comprising a pair of coils 12 and 14 woundaround an annular stator core 16 within a housing 18. Within stator core16 and coils 12 and 14 and spaced therefrom is a permanent-magnet rotor20.

When it is desired to lower cutter head assembly 50 into position toscore the piece of glass G, current is supplied from a source E througha fixed resistance R and a variable resistance R,,,. Switches S and Sare closed and switches S and S, are opened (as shown in FIG. 2). Theamount of current supplied to motor can be minimized by increasing theresistance in variable resistor R This is very important since it allowsone to both reduce the force with which the cutter initially engagesglass G and control the force with which the cutter scores glass G.Further, capacitor C is placed in parallel with motor 10 to delay thesupply of current to motor 10. The size of capacitor C is chosen so thatlittle current is supplied to torque motor 10 until the cutter contactsthe piece of glass G. This also reduces the force with which the cutterinitially engages glass G. As this small amount of current is suppliedto torque motor 10, a counter-EMF is generated within the torque motorto oppose a rapid rotation of permanentmagnet rotor 20. The forceactually supplied to the cutter before it engages the glass is verysmall (about 1 pound).

The passage of direct current through the coils 12 and 14 generateswithin the motor 10 a suitable electrical field, tending to influencethe location of the rotor 20, which is made of a permanent-magnetmaterial such as an Alnico alloy of high energy product. The rotor has anorth pole 22 and a south pole 24. It also has a central opening 26which can be threaded to receive shaft 30. When the rotor 20 is in theposition indicated in the dash-dot lines in FIG. 2, and direct-currentis supplied to the torque motor (with switches S and S closed andswitches S and S open, as illustrated in FIG. 2), there is exerted uponthe rotor 20 a force that tends to turn the rotor 20 to the positionindicated in solid lines in FIG. 2.

It must be kept in mind that there is a direct relationship between theposition of rotor 20 and the location of the cutter head assembly 50.When rotor 20 is in the position indicated by dash-dot lines in FIG. 2,cutter head assembly 50 is spaced from the piece of glass G as indicatedby dash-dot lines in FIG. 3. As rotor 20 moves to the position indicatedby solid lines in FIG. 2, the cutter head assembly 50 moves intoposition to score the piece of glass G, as indicated by the solid linesin FIG. 3. This is because the cutter head assembly 50 is rigidlyattached to block 40 which is rigidly mounted on shaft 30 which isrigidly mounted with rotor 20.

After score line 2 has been completed and it is desired to raise cutterhead assembly 50 to the position shown in dash-dot lines in FIG. 2,switches S and 5;, are opened and switches S and S, are closed (notillustrated). This has the effect of reversing the polarity on torquemotor 10 so that direct current is supplied in an opposite direction toreturn rotor 20 to the position in dicated by dash-dot lines in FIG. 2.The resistance in variable resistor R can be adjusted to vary the amountof current supplied to torque motor 10 to raise cutter head assembly 50.This variable resistor, together with capacitor C, controls the ratewith which the cutter head assembly 50 is raised.

FIGS. 4, 5 and 6 indicate various details of the apparatus made inaccordance with the present invention. Referring to FIG. 4, there isillustrated the details of a typical cutter head assembly 50. Assembly50 includes a cutting wheel 52 mounted on a pillar post 56 by a wheelaxle 54. Cutting wheel 52 can be made of any standard material such assintered tungsten carbide, possibly having a diameter such as 56 inch(about 3 millimeters) or less with a cutting angle such as about orless. Pillar post 56 is mounted within body 58. Bearings 60 allow pillarpost 56 and therefore cutting wheel 52 to pivot within body 58.Shaft-like portion 62 extends upwardly from the top of body 58.

Referring to FIGS. 5 and 6, there is shown a block 40 having holes 42and 44 extending therethrough, and a shaft 30 with threaded end portions32 for mounting shaft 30 in the threaded central openings 26 of therotors 20, respectively.

In operation, shaft-like portion 62 of cutter head assembly 50 isinserted into hole 42 of block 40 and any suitable means, such as allenscrews 46 maintain shaft- Iike portion 62 (and therefore cutter headassembly 50) in position within block 40. Hole 44 is sized to receivecentral portion 34 of shaft 30. Longitudinal projection 36 fits intoslot 48 to prevent shaft 30 from rotating within block 40. Allen screws38 prevent shaft 30 from sliding within block 40.

Those skilled in the art will understand that, in most instances, it isessential that the force exerted by the cutter head upon the glass be onthe order of IO pounds, and preferably about pounds or more, in orderthat a score of suitable depth may be obtained. If the wheel containedin the cutter head assembly is extremely sharp, it will, in someinstances, be possible to use a lesser pressure. On the other hand, itis desirable not to use a pressure so great as to cause immediatefracturing of the glass being cut throughout its thickness.

For the most part, it is desirable that the score (except when thecross-cutting of a glass ribbon, complete with edge portions and/or edgebulbs, is beingpracticed) be located at a suitable distance with respectto the piece being scored for cutting, such as a minimum of 6 or 8 timesthe thickness of the glass.

The present invention has particular importance in connection with thecutting of a large sheet or ribbon of glass into a plurality of segmentsby means of a plu rality of cutter heads located upon a cutter bar. Inaccordance with prior-art practices, it has been hitherto considerednecessary either to use the pneumatic system, with its attendant dangersof the kinking or the wearing of the cords or lines connecting thepneumatic supply source to the cutter heads, or to use a springloadedapparatus, with its attendant difficulty that it is inconvenient toadjust the spring means associated with each of the cutter heads so thatscore line of adequate and desired depth is obtained.

Although the invention has been described in connection with adirect-current torque motor, it will be apparent to those skilled in theart that other suitable constant-reluctance motor means may be devisedand used. What is required is that there be provided an electrical ormagnetic means that operates on the basis of a substantially constantair gap and a substantially constant environment of magneticpermeability. This is to be distinguished from the use of anelectromagnet or solenoid where the air gap goes from a substantialvalue such as of an inch (about 3 millimeters) or more to substantiallyzero, possibly with occasional excursions thereafter of up to 1/12 of aninch (about 2 millimeters). With the use of such equipment, it issubstantially impossible to exert a constant force, as is contemplatedin accordance with the principles of the present invention. I

Those skilled in the art of cutting glass will appreciate from theforegoing disclosure that remarkable novel effects can be obtained ifthe series of sheets or moving ribbon is cut by means of a set ofcutters of the kind taught above that operate, one set transversely ofthe glass in its travel, and one set longitudinally, with thepositioning of the cutter heads being automatically controlled and withthe cutter heads being raised or lowered at precisely chosen moments.The actuation is so quick and precise that it becomes possible toenvision using interrupted-cut practices that were hitherto impractical.The losses, in changing from one pattern of cutting to another, are muchreduced. With the faster and more reliable action obtained with thepresent invention, it is possible to cut more closely around a defect,so that less glass is discarded. The cutting of flat glass to meet acustomer's size specification may be accomplished substantially moreefficiently, rapidly and conveniently when the instant invention ispracticed.

I claim as my invention:

1. An apparatus for the scoring of glass comprising:

a. an adjustable source of electric current,

b. a constant-reluctance motor means operatively connected to saidsource of current, and

c. a cutting means for scoring said glass, said cutting means beingrigidly connected to a rotatable mov'- able member within saidconstant-reluctance motor means.

2. An apparatus as defined in claim 1, characterized.

in that said constant-reluctance motor means comprises a torque motor.

3. An apparatus as defined in claim 2, characterized in that saidmovable member comprises a rotor.

4. An apparatus as defined in claim 3, characterized in that said torquemotor is a direct-current torque motor.

5. An apparatus as defined in claim 4, characterized in that a capacitoris placed in parallel with said torque motor to reduce the current onmotor as said cutting means is moved into position to score said glass.

6. An apparatus as defined in claim 4, characterized in that saidadjustable source of electric current includes a variable resistor.

7. An apparatus as defined in claim 6, characterized in that a capacitoris placed in parallel with said torque motor to reduce the current onsaid motor as said cutting means is moved into position to score saidglass.

8. An apparatus for the cutting of glass comprising:

a. an adjustable source of electric current,

b. a constantqeluctance motor means operatively connected to said sourceof current, and

c. a cutting means for cutting said glass, said cutting means beingrigidly connected to a rotatable movable member within saidconstant-reluctance motor means.

9. An apparatus as defined in claim 8, characterized in that saidconstant-reluctance motor means comprises a torque motor.

10. An apparatus as defined in claim 9, characterized in that saidmovable member comprises a rotor.

11. An apparatus as defined in claim 10, characterized in that saidtorque motor is a direct-current torque motor.

12. A method of producing a score line of predetermined depth upon asheet of glass comprising:

a. moving said sheet of glass with respect to a cutter head means, and

b. actuating a constant-reluctance motor means to rotatably urge saidcutter head means into a surface of said glass sheet.

13. A method as defined in claim 12, characterized in that said motormeans comprises a torque motor.

14. A method of severing a piece of glass comprising:

a. moving said sheet of glass with respect to a cutter head means, and

b. actuating a constant-reluctance motor means to rotatably urge saidcutter head means into a surface of said glass sheet.

15. A method as defined in claim 14, characterized in that said motormeans comprises a torque motor.

16. A method of severing a piece of glass comprising:

a. moving said sheet of glass with respect to a cutter head means,

b. actuating a constant-reluctance motor means to rotatably urge saidcutter head means into a surface of said glass sheet, and

c. applying a bending moment about a score line produced by said cutterhead means.

17. A method as defined in claim 16, characterized in that said motormeans comprises a torque motor.

1. An apparatus for the scoring of glass comprising: a. an adjustablesource of electric current, b. a constant-reluctance motor meansoperatively connected to said source of current, and c. a cutting meansfor scoring said glass, said cutting means being rigidly connected to arotatable movable member within said constant-reluctance motor means. 2.An apparatus as defined in claim 1, characterized in that saidconstant-reluctance motor means comprises a torque motor.
 3. Anapparatus as defined in claim 2, characterized in that said movablemember comprises a rotor.
 4. An apparatus as defined in claim 3,characterized in that said torque motor is a direct-current torquemotor.
 5. An apparatus as defined in claim 4, characterized in that acapacitor is placed in parallel with said torque motor to reduce thecurrent on said motor as said cutting means is moved into position toscore said glass.
 6. An apparatus as defined in claim 4, characterizedin that said adjustable source of electric current includes a variableresistor.
 7. An aPparatus as defined in claim 6, characterized in that acapacitor is placed in parallel with said torque motor to reduce thecurrent on said motor as said cutting means is moved into position toscore said glass.
 8. An apparatus for the cutting of glass comprising:a. an adjustable source of electric current, b. a constant-reluctancemotor means operatively connected to said source of current, and c. acutting means for cutting said glass, said cutting means being rigidlyconnected to a rotatable movable member within said constant-reluctancemotor means.
 9. An apparatus as defined in claim 8, characterized inthat said constant-reluctance motor means comprises a torque motor. 10.An apparatus as defined in claim 9, characterized in that said movablemember comprises a rotor.
 11. An apparatus as defined in claim 10,characterized in that said torque motor is a direct-current torquemotor.
 12. A method of producing a score line of predetermined depthupon a sheet of glass comprising: a. moving said sheet of glass withrespect to a cutter head means, and b. actuating a constant-reluctancemotor means to rotatably urge said cutter head means into a surface ofsaid glass sheet.
 13. A method as defined in claim 12, characterized inthat said motor means comprises a torque motor.
 14. A method of severinga piece of glass comprising: a. moving said sheet of glass with respectto a cutter head means, and b. actuating a constant-reluctance motormeans to rotatably urge said cutter head means into a surface of saidglass sheet.
 15. A method as defined in claim 14, characterized in thatsaid motor means comprises a torque motor.
 16. A method of severing apiece of glass comprising: a. moving said sheet of glass with respect toa cutter head means, b. actuating a constant-reluctance motor means torotatably urge said cutter head means into a surface of said glasssheet, and c. applying a bending moment about a score line produced bysaid cutter head means.
 17. A method as defined in claim 16,characterized in that said motor means comprises a torque motor.